1) Can you describe how it's not working? If the plugin is maintaining the WordPress standard, it should also generate those image sizes. You can check in the upload folder if its generating those images or not.

2) Use this code in your themes single.php to show featured images:
[php]
if ( has_post_thumbnail() ) {
the_post_thumbnail( ‘thumbnail' );
}
[/php]

For example, if I add a IMAGES field into my form, so users can submit images (not FEATURED IMAGES).
They show if I put [GALLERY] shortcode manually, but I need to display automaticaly customizing my theme.